This invention relates generally to electrical transformers and more particularly, but not by way of limitation, to an electrical transformer having one winding split into two parts which have one or more additional windings radially disposed therebetween, the additional winding or windings having sections connectable in parallel, which sections when in parallel are spaced equal total radial distances from the two parts of the split winding.
In U.S. Pat. No. 3,083,331 to Spurway, it is disclosed that a transformer is to be constructed so that corresponding sections of the windings have equal "leakage impedances." Having equal leakage impedances (more correctly, leakage reactances) is a desirable criterion for a transformer because losses are thereby reduced; however, the attainment of such a criterion requires a relatively complex manufacturing process for constructing the transformer. For example, equal leakage reactance requires that the number of turns in each winding section be equal, the occupied space of each section be equal, the turn lengths be equal, and the primary/secondary spacing be equal.
In U.S. Pat. No. 4,160,224 to Owen there is disclosed a transformer which can be more easily manufactured than the Spurway transformer; however, the transformer disclosed in the Owen patent does not have equal leakage reactances. Despite the unequal leakage reactances and contrary to the disclosure in the Spurway patent that leakage reactances must be equal, the transformer disclosed in the Owen patent is operable. Although the transformer disclosed in the Owen patent is functional, it operates with relatively increased losses due to the unequal leakage reactances. The tradeoff for these losses is a more easily manufacturable, and thus likely less expensive, transformer.
The transformer disclosed in the Owen patent includes axially spaced, side-by-side subwindings having electrically parallelable sections which are spaced different radial distances from the other windings. These windings are co-directionally wound for easier fabrication, but they are disposed so that some measurable amount of loss occurs due to the unequal leakage reactances. Additionally, the side-by-side construction of the windings causes the transformer to have a relatively weaker short-circuit strength because significant axial forces can be developed as a result of such offset design of the paralleled sections (and also the corresponding offset design of any remaining seriesed sections). These axial forces have a destructive telescoping effect on the transformer windings and are not as easily containable as are radial forces.
Although it is known that a relatively easily manufacturable transformer having unequal leakage reactances can be functional, it is desirable to construct an improved transformer which reduces the losses caused by the unequal leakage reactances and which reduces or prevents the destructive axial forces arising during short-circuit conditions. It is further desirable to achieve these ends while still retaining a transformer which is relatively easily manufactured.